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    <h3>全局选择器: *</h3>
    <h3>元素选择器:标签名称</h3>
    <h3>类选择器:class 属性名 (.)</h3>
    <h3>id选择器：id属性名(#)</h3>
    
    <P class="=text" id="desc">我是p标签内容</P>
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